Continuous mining machine

ABSTRACT

A continuous mining machine includes a main frame mounted on tracks for mobility, a cutter head mounted on a subframe which is adapted to be moved toward and away from the front of the main frame, a conveyor to collect mined material and convey it to the rear of the main frame, and a roof bolter supported on the main frame adjacent the front thereof, whereby, as the sub-frame is moved away from the front of the main frame and the cutter head mounted thereon operates to cut material to be mined, thereof bolter is simultaneously operated to perform roof bolting operations close to the face of the mine.

TECHNICAL FIELD

This invention relates to continuous mining machines.

BACKGROUND ART

With reference to FIG. 1 of the drawings, the most common method ofcutting coal and supporting the roof used in Australian coal mines forroadway driveage uses timber props 10 set at each side of the roadway 11beneath or adjacent to steel straps, wooden bars or similar devices 12held to the roof by roof bolts 13. The straps or bars 12, are usuallysupplied cut to the required length to suit the roadway width andusually with pre-drilled holes at the desired roof bolt positions. Props10 are usually supplied over-size, cut to length on site and installedby hand using wooden wedges to tighten them in position. Roof bolts 13are steel rods 14 of the required length supplied with an anchoringdevice 15 (most commonly a resin type of glue) to fix one end in therock, and a threaded outer end to take a nut 17 and steel washer 16.Their action is to clamp the layers of roof strata together to form astrong beam and/or to suspend layers of broken strata from more stablehigher layers.

To install a roof bolt, a small hole (usually of the order of 27 mmdiameter) is drilled into the rock to the length of the bolt. Acartridge containing a two part resin mix is then inserted into the holeand pushed to the end using the bolt itself. The bolt is then spun for afew seconds. This has the effect of breaking-up the cartridge and mixingthe resin parts. Because of the fast-setting nature of the resin, thenut can be tightened almost immediately to bear against the roof strap,bar, etc., and a degree of tension is thus applied to the bolt. The samemachine is normally used to drill the hole, install the bolt and tightenthe nut using various adaptors fitted to the chuck. During installationof the first two bolts the strap, bar, etc., is normally held inposition by two hydraulic jacks attached to the mining machine. Thedrilling machines are commonly hand held machines supported on anextendable leg, but can be attached to the mining machine.

It should be noted that there are wide variations in the systemdescribed above in number, type, and spacing of supports and bolts,types of bolt anchoring systems, and angle at which bolts are installed.These variations depend on a number of factors, notably surrounding rocktypes and strengths, roadway heights and widths, and stress conditions.However, the basic system is the same in the majority of cases.

The machine which actually cut the coal, the continuous miners, come ina variety of makes and models, but are all basically the same inprinciple. The main frame which supports the working parts and containsmotors, hydraulic pumps, tanks, controls, etc., is mounted on a crawlertrack assembly for mobility. At the top of the front of the machine ismounted the cutting head which has rotating drums and/or chains fittedwith cutter picks to cut the coal. In the current range of machines thehead is usually referred to as fixed which means it cuts a set widthalthough it can be raised and lowered to cut the desired height. The cutcoal falls to the floor where it is picked up by a loader apron fittedwith some type of gathering device which guides the coal into the centreof the machine. From here the coal is collected by a scraper conveyorwhich runs through the centre of the machine to a luffing and slewingjib which enables the coal to be loaded into mobile vehicles (shuttlecars) behind the miner for transportation to the conveyor belt system.

Because the machiens can only cut approximately their own width at onetime it is necessary to move them around to cut the full width required.Also, in order to cut forward the whole machine has to tram into theface. It therefore follows that while coal cutting operations are inprogress the whole machine is almost continuously moving in a confinedarea. This makes it very hazardous, if not impossible, to work alongsidethe machine while it is cutting and it is in this confined area that theroof support operations have to be carried out. As a consequence thewhole process becomes cyclic whereby a certain amount of coal is cut andmining operations then cease while roof support is carried out.

The need for the whole machine to move while cutting also precludes theuse of miner mounted drill rigs and temporary supports during thecutting time.

The delay caused to coal cutting by this cyclical nature of operationsvaries according to the degree of support required in the givenconditions, but is commonly of the order of 30% of available time.

It is therefore an object of the present invention to provide acontinuous mining machine which minimizes the delay to coal cuttingcaused by positioning of the roof supports, and such that the miningprocess will become more continuous.

Because of the wide range of variations in seam thickness, strata andstress conditions (and hence support requirements) and mining methods,it is impractical to develop one machine to cover all requirements. Theaim of the present invention is to cover the most common situations andmines with additional or less requirements being treated as specialcases requiring modifications to the basic machine, or variations in themethod of use which may affect its ability to mine continuously.

These basic parameters for the machine are as follows:

(a) Ability to cut and support continuously in seams up to 3.0 m thickwith supports 1 m apart, with the time taken to install supports being 5mins. This leads to a necessary maximum cutting rate of 4.2 tonnes/minfor a 5.0 m wide roadway (coal density in the solid of 1.4 tonnes/m³).

(b) Increase production and rate of advance in development headings.

(c) Ability to install up to 4 roof bolts simultaneously. Anyrequirements for less would not present a problem as rigs could beomitted. Requirements for more would be special cases where additionalbolts would have to be installed either behind the machine or bydelaying production. Even in the latter case improved production wouldbe expected in comparison with current methods.

(d) Capability of operation in a 4 m wide roadway, but with the abilityto cut a variety of greater widths if required.

(e) Ability to roofbolt within 1 m of the face for at least some of thebolts which may require some flexibility in roofbolter mountings.

(f) Incorporation of a minimum working height of 1.5 m, although 2.0 mwould be acceptable for most cases.

(g) Provision of a maximum machine width of 2.4 m and length of around12 m; articulation to be used if a greater length is required.

(h) Design for a maximum weight of 50 tonnes. Any requirements forseparation to be as simple as possible, and any parts removed to beeasily handled; articulation may be an advantage here provided bothhalves are able to tram individually. Also to aim for a maximum floorloading of 165 kPa.

(i) Design the machine for ease of access to all parts for maintenancepurposes.

More importantly, and in accordance with the basic objective of thepresent invention, it is required that the roof bolters be an integralpart of the machine.

The mining methods performed with existing equipment, involve eitherproviding a machine essentially in two parts, whereby a stable platformis provided for roof support operations by one part while the othercontinues to cut coal, or alternatively two separate machines able towork in the same area, removing roof support operations from the facearea while production is in progress. The latter operation can be doneby cutting coal for a period at one face and then moving to another facewhile the first is supported. Alternatively, temporary supports can beinstalled to hold the roof and permanent supports installed a distancebehind the cutting operations.

The moving of equipment to another face is only practical if thedistance advanced before moving is reasonably great. There are few minesin Australia where roof conditions are suited to this system. The timespent tramming from place to place also introduces an additional elementof non-productive time. The option of setting temporary supports hasbeen attempted in several mines. The use of relatively light hand-setsupports is generally inadequate to control the roof in places whereroof bolts are ultimately required. This led to the development of largeframe type supports across the roadway which were self-advancing in amanner similar to longwall chocks. Such units, however, suffer from twomajor disadvantages. Firstly, the self-advancing action of the supportsnecessitates continuously loading and unloading the roof strata whichcauses it to break up, and in itself can lead to poor roof conditions.Secondly, the frame structure has to be large and is therefore unable tonegotiate a bend of suitably small radius in the roadway, that is, it isonly suited to single heading development. A further possibledisadvantage is that although roof support operations are removed fromthe immediate face area they still have to be carried out in the initialcoal transport area. Thus, there is still a potential for the operationsto interfere with production and become hazardous, particularly ifshuttle cars are used.

For the above reasons, it is clear that such a method is not practicalfor most Australian mines.

It is therefore intended, with the machine of the present invention, tofollow the alternative procedure of providing a single machine to allowfor roof support operations as well as continuous cutting of the coal.Machines presently available incorporating provision to perform bothfunctions are the Joy 1CM and 6CM as supplied by Joy ManufacturingCompany Pty. Limited. These machines have a cutting head similar topresent continuous miners but mounted on a turntable with fore and aftslides fixed to the body of the machine. After tramming the machine upto the face the head can be sumped in using the slides, and by raisingand lowering the cutting head and slewing on the turntable, the fullroadway profile can be cut for a certain increment of advance while thebody of the machine remains stationary. While the principle of beingable to work alongside the machine whilst cutting is satisfied, and astable bolting platform could be provided, it has been found that thelength of head required to reach the full profile of the roadway meantthat the bolts could, at best, only be installed up to 2.5 to 3 m fromthe face. Such unsupported spans may be acceptable in some mines butthere are many cases where this would lead to serious loss of roofcontrol.

The same problem exists with roadheader styles, of machines such assupplied by Voest Alpine (Australia) Pty. Limited (VOEST-ALPINE AM75).With such a machine the long arm necessary to cut the desired roadwayprofile requires that any bolting system be sited outside the arc, whichthe arm must cover, in order to be able to bolt and cut at the sametime. Additionally, many of the roadheader style machines do not have ahead which can sump forward, the sumping action being carried out bytramming the whole machine forward. This precludes any roof supportfunctions being carried out from the frame of the machine at leastduring the sumping action.

Consideration has therefore been given to types of machines that eithercut the full profile of the roadway in a planing or milling action witha short depth of cut, or need a relatively small cutting head mounted ona device which could be manoeuvred in a vertical plane parallel to theface to profile the full size required.

Such a style is the borer miner as developed by Goodman and Mariettacommonly known as the Goodman Borer Miner. Such machines cut arectangular profile with rounded corners and, to some extent, roundedsides in one pass. However, whilst such machines cut a uniformly sizedand stable profile, they suffer from a number of disadvantages. Themachines are notoriously difficult to steer satisfactorily in thevertical plane and cannot negotiate a very sharp turn in the horizontalplane, whilst they are unable to cope with large variations in seamheight. Because of the mass of machine required to thrust the head intothe coal to cut the full profile in one pass, such machines are also notsuited for the attachment of roof support equipment close to the face.

A similar style of machine to the Goodman Borer, is known as the DoscoIn Seam Miner. This machine cuts an oval profile roadway using anendless chain type of cutter around the periphery of the machine. Theunit is not track mounted but rests on the floor, and is moved forwardby hydraulic pusher rams reacting against hydraulic chocks set betweenroof and floor behind the machine. This configuration provides theability to carry out roof support operations very close to the face.However, the cutting height is limited to around 1.8 m which is notsatisfactory for most Australian mines. Also, being floor mounted, themachine is unable to negotiate sharp horizontal curves and isessentially a single entry machine.

Two other styles of machines with a relatively small cutting head andmoveable in a vertical plane parallel to the face, are the EickhoffESA60-L and the Westfalia VMO8.

The Eickhoff ESA60-L consists of a small ranging arm shearer mounted ona short section of armoured conveyor. The shearer can be moved acrossthe conveyor to be able to cut the desired roadway width, and the armcan be raised or lowered to cut the desired height. At the end ofmachine travel the arm is swung round in a vertical plane, thus cuttinga semi-circular profile on the roadway sides. The conveyor section restson the floor and forward advance is obtained by the use of hydraulicrams similar to the Dosco In-Seam Miner. While this style of machinecould be track-mounted to obtain better manoeuverability, and alsoallows roof supports to be set close to the face, it too suffers from anumber of disadvantages. The cutting drum cannot be sumped in directlyand the head must be angled across the face so the sumping action iscarried out across the face width. The advance of the machine therebybecomes a shuffling action where only one side is advanced at a time.The large radius curved sides, while having some support benefit, arenot amenable to setting timber and require a very wide effective roadwayin order to obtain sufficient width of flat floor for most purposes,especially in thick seams.

The Westfalia VMO8 is a small cutting head style of machine which hasbeen developed. This heading machine is a floor mounted machine with acutter head, somewhat similar to that on a continuous miner, carried onan armoured conveyor. The cutting style of this machine has theadvantages of allowing supports to be set close to the face, cutting astraight-sided roadway amenable to minimizing width and the use oftimber supports, and producing a concave face in the vertical planethereby reducing the unsupported roof span ahead of the supports.

The cutting head of the Westfalia machine consists of two cylindricaldrums attached to each end of a T-shaped arm able to range verticallywithin limits governed by the maximum cutting height required. The drumsare constructed in the form of two spoked wheels connected by a seriesof six blades around the periphery. Cutter picks are attached on theouter circumference of the wheels, on the outside surfaces of thecylinder sides and on the outer edges of the blades, so that the drumscan cut in any direction. The direction of rotation is such that the topof each cutting drum moves towards the face, and in this way the bladessupply a loading action for the cut coal onto the conveyor. The machineis designed to be able to cut up to 125 mm below the floor.

The drive motor for the cutter head is 90 kW hydraulic motor mounted onthe axis of rotation of the ranging arm, driving through a chain driveonto a common shaft for the cutter drums. The cutter drums are 0.9 mdiameter and the peripheral speed is variable between 0 and 5 m/sec(rotation approximately 0 to 106 rpm).

The vertical ranging action of the head is controlled by a hydrauliccylinder mounted between the cross-member of the T-shaped arm and thehead support frame.

The head support frame is mounted on a trapped rail system which formspart of the face conveyor; the head is thus free to travel in adirection parallel to the face. Travel in this direction is controlledby a chain driven by a hydraulic motor mounted on one end of the faceconveyor, with adjustable speed from 0 to 13 m/min.

The conveyor system of the Westfalia machine is a scraper chain in theform of a T, the cross-member of which forms the face conveyor and alsocarries the trap rail system for the head support frame. The scraperchains are single strand with flights cantilevered out to one side, andare trapped in a groove on the rear side of the face conveyor. The faceconveyor also has a ramp plate on the leading edge to enable pickup ofcoal not loaded by the action of the cutter drums.

Separate scraper chains operate on each side of the machine and at thethroat (usually, but not necessarily, in the centre of the machine) areguided through 90° and run up the delivery section, the flightsinterspacing in the same fashion as the teeth of a zip fastener. Theconveyor chains are hydraulically driven on a common shaft from thedelivery end of the system. Depending on the chain speed the conveyorcapacity is 200 to 250 tonnes/hour.

On the outer ends of the cross-member of the T-Conveyor are hingedskids, operated by hydraulic cylinders, which are able to bear againstthe rib sides and so prevent the body of the machine being pushedsideways.

Forward thrust is applied to the cutter head by two large hydraulic ramsmounted to the rear of the face conveyor, and reacting against hydraulicchocks set between roof and floor in the roadway behind the machine. Aswell as supplying a reaction point for the rams, these chocks also havea temporary roof support function, the permanent supports being setbehind them.

The hydraulic chocks are self-advancing similar to chocks used onlongwall faces. They can also be used to drag forward the power packsand main conveyor as the machine advances.

Power is supplied from 2×90 kW power packs, one to supply the cuttermotor, the second for the conveyor drive, hydraulic chocks and hydraulicrams.

To minimize dust in the working area, 2×500 mm diameter exhaust ductsare permanently mounted from the hydraulic chocks with a flexiblesection leading back to the main duct or brattice line.

At the start of a cutting cycle with the Westfalia machine the head isat floor level against the face. To sump, the machine is pushed forwardby the hydraulic rams, and both cutting drums cut into the face in thedirection of face advance. The depth of sump is approximately 0.3 m andis governed by the distance from the front edge of the cutting drums tothe cross-member of the T-shaped ranging arm.

On completion of sumping, the head is pulled across the full width ofthe heading. Initially, cutting is carried out by the outer edge of theleading drum and the inner edge of the trailing drum until the core ofcoal formed between the drums is removed. From this point on only theleading drum is cutting. After cutting the full width the head is raisedto the next level and traversed back across the width of the roadway.This process is repeated for another one or two passes, depending on theseam height, until the full cross-section has been cut. The head is thendropped back to floor level and a clean-up run is made across the face.

Finally, the machine is pushed forward again by the pusher rams to beginthe cycle once more. The self-advancing supports may be moved forward atany convenient time during the number of cycles allowed by the fullstroke of the pusher rams.

An alternative method with the Westfalia machine is to oscillate thecutting head during the sumping operation so that the core is removed inthe sumping process thereby allowing a deeper sump, up to about 0.5 m.The remainder of the cycle will be carried out in the same way asbefore, but with a correspondingly larger depth of cut. This methodenables more coal per machine traverse to be obtained, but the depth ofsump possible will be dictated by the nature of the coal being cut andthe power available.

Other cutting patterns could be used, the most suitable depending on thenature of the material being cut and the conditions at the face.

However, although the Westfalia works satisfactorily in principle andproduces a good roadway, it suffers from a number of problems.

In one mine roof bolting was carried out behind the machine after acertain distance of advance had been achieved. Ultimately, a major falloccurred behind the machine, burying much of the equipment. It isconsidered that the major cause of the fall was the delay ininstallation of the roof bolts, and this was no doubt exacerbated by thecycling of the roof by the hydraulic chocks associated with the machine.

One major drawback of the Westfalia machine is the low productionpotential, which is only of the order of 1-2 tonnes/min., and its slowrate of advance.

In another mine a Westfalia machine was modified by mounting thehydraulic pusher rams on a Joy 6CM chassis.

Trials with the modified machine were successful in that the track framewas able to provide a sufficiently stable base for sumping the cuttinghead, and the roadway proved to be very tidy and stable. Miningconditions were also improved greatly over those existing in adjacentroadways. However the rate of advance of the machine was notsatisfactory, and it has been withdrawn from service.

From a consideration of all the machines presently available it wasapparent that a machine based on the principle of the Westfalia VMO8 hasthe greatest potential to satisfy the objectives, provided the problemstherewith could be overcome and in particular provided a greaterproduction rate can be attained. The main points in favour of aWestfalia style of machine are as follows:

(a) Permanent supports can be set close to the face, probably within 1to 1.4 m.

(b) The machine would cut a straight rib and a roadway width which willbe constant. This would lead to improved roadway stability and isamenable to setting timber supports, if required, close to the rib. Italso provides the minimum roadway width for a given width of flat floor.

(c) The face would be cut with a concave shape from roof to floor, whichreduces the effective span of unsupported roof in front of the machine.

(d) The cutting action is relatively gentle and in small incrementswhich again aids roadway stability and can be advantageous in gassyseams.

(e) Much of the machine can be made up from items of already provendesign.

(f) The style of machine has been trialled and was successful inprinciple.

DISCLOSURE OF THE INVENTION

The present invention therefore envisages a continuous mining machine,comprising a main frame mounted on tracks for mobility, a cutter headmounted on a sub-frame which is adapted to be moved toward and away fromthe front of said main frame, conveyor means to collect mined materialand convey it to the rear of said main frame, and roof bolting meanssupported on said main frame toward the front thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

One preferred embodiment of the invention will now be described withreference to the accompanying drawings; in which:

FIG. 1 is a sectional view of a mine roadway illustrating a commonlyknown technique for cutting coal and supporting the roof, as describedpreviously.

FIGS. 2 and 3 are two side elevation views of the general arrangement ofthe machine of this preferred embodiment of the invention showing thetwo head sumping positions.

FIG. 4, is a plan view of the machine of FIG. 2 in the extended headposition.

FIGS. 5 and 6 are enlarged side elevation views, with the roof boltersomitted for the sake of clarity, of a mechanism incorporated in themachine to enable the machine to negotiate changes in floor grade,traverse changes in floor horizon, and raise the front section forflitting, and

FIGS. 7 and 8 are enlarged side elevation views showing the details ofthe roof bolters as mounted on the machine of the preceding drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

In basic design and principle of operation, the cutting head 21 mountedon a cutter head support frame 26 is the same as the Westfalia VMO8,having a cutter head 21 incorporating cutter drums 24, pivotable rangingarm 22, pivotable under the action of a head ranging ram 25 and cuttermotor 23 which drives the shaft for the cutter drums via a multi-linkchain drive extending through the ranging arm 22. Increased power isachieved by the use of a large motor (estimated to be of the order of100 to 110 kW), and associated strengthening of supports and drivecomponents. A maximum pick speed in the order of 1.2 m/sec is considereddesirable in minimizing dust and reducing the risk of frictionalignitions of methane.

Another variation from the Westfalia VMO8 design relates to the overallwidth of the cutting head. As discussed hereinafter, the overall widthof the face conveyor system may need to be easily reducible tofacilitate turning away and retraction of the machine from the workingface when necessary. This will result in being unable to extend thetrain rail system to extremities of the face conveyor. In order to beable to cut a sufficient distance beyond the width of the machine, theoverall width of the cutter head may be extended and/or the width of thehead support frame reduced. The extent to which this can be done isaffected both by stability and strength considerations, and by the factthat the distance from the inside edge of one cutter drum to the outsideedge of the other must be less than half the total roadway width, inorder to be able to cut out the core between them.

The leading zipper conveyor 28 having a face section 28a of theWestfalia VMO8 has been retained in the basic design with certainadditions. In order to be able to negotiate a turn with the machine, itis desirable to have the swivel or slew conveyor 29 at the rear. Whenthe conveyor 29 is swivelled, there is a difference in length betweenthe outer and inner sides of the curve. With the "zipper" type ofconveyor 28, such a difference is not acceptable because the two chainswould become unsynchronised, and the flights would foul and jam at thethroat of the machine. Therefore, the machine has the two separateconveyors, 28 and 29. The front "zipper" type 28 loading onto the secondtype 29 in the centre of the tracked main frame 30. The second conveyor29, being a centre strand type, is therefore able to swivel at 100 underthe action of two rams, 101 and 102 one on either side of the swivel 100and coupled between the main frame 30 and the tailing section of theslew conveyor 29. Hydraulic motors 103 at the trailing end of the zipperconveyor 28 serve to drive the two flights of that conveyor, whilstelectric motors 104 on the trailing end of the slew conveyor serve todrive that conveyor. The slew conveyor 29 is also pivotally mounted inthe main frame 30 so as to be capable of being tilted up and down aboutthe pivot by means of a hydraulic ram 123 coupled between the main frame30 and the conveyor 29.

The front section of the machine comprising the zipper conveyor 28 withits face sections 28a and cutter head support frame 26 is mounted to themain frame 30 so as to be extended forwardly of the main frame 30 duringcutting operations whilst the main frame 30 remains stationary, andbecause the front conveyor 28 would move forward with the cutting headwhile the rear 29 would remain stationary with the track frame 30, thetwo conveyors overlap by the maximum advance of the head relative to thetrack frame 30.

The face conveyor section 28a needs to be close to the full width of theroadway in order to ensure good clean-up and to avoid leaving coal inthe ribs. However, in order to turn away, it is desirable to be able toreduce this overall width without reducing the reach of the cutting head21. It is also necessary to be able to reduce this overall width inorder to retract the machine for repairs and maintenance, or to move toanother working place. It would be possible to make provision for thisshortening by having bolt-on sections (not shown) on each end of theface conveyor 28a, although this would entail a major operation eachtime. It is therefore envisaged that the final section of each side ofthe face conveyor 28a be replaced by a short section containing anothertype of loading device, which can be readily retracted or folded up bythe use of hydraulic cylinders. The type of device could be simply adozer blade or small spinner disc (not shown).

In order to minimize the number of joints, the centre section of theface conveyor 28a on which the cutting head 21 is mounted for movement,on upper and lower rails 30a, by a motor driven chain drive 105 (seeFIG. 4), would be manufactured in one piece to the same width as mainframe tracks 30b. The next section (on each side) would be bolted on, sothat they could be removed for transport into and around the mine.

In the machine envisaged, all the parts so far described, with theexception of the rear conveyor 29, would be designed to be advanced acertain distance (e.g. 1 meter) while the main track frame 30 of themachine remains stationary. In order to do this, one proposal is thatthe conveyor section 28, with the cutting head 21, be mounted on theends of two large hydraulic sumping rams 106. The cylinder pistons arepin-jointed at 107 onto the support frame 26 for the conveyor 28 and at108 onto the main frame 30. Two smaller lift cylinders 38, pivotablymounted on either end (109 and 110), are provided to enable the faceconveyor 28a and head 21 to be lifted off the ground, so that themachine can be retracted from the face and trammed to another site (seeFIGS. 5 and 6). The trailing end of the frame for the conveyor 28 isslidably mounted at 111 to enable movement relative to the main frame 30and is retained against separation by a ball joint 112 to allow fortilting of the conveyor when the face conveyor 28a and cutting head 21are lifted off the ground.

In certain circumstances the sumping rams 106 may be very prone todamage by twisting from any high loads on the extremities of the faceconveyor section, or from any uneven floor conditions. To overcome thisthe sumping rams 106 are pin-jointed at both ends, that is, at 107 and108, with spherical bearings and therefore free to move relative to eachother in the vertical plane. With this system, the sumping rams 106 donot carry any vertical loads. The cutter head 21 and front conveyorsystem 28 would be supported entirely on the floor, and would merelytransmit horizontal thrust.

For stability, the sumping rams 106 would be mounted approximately alongthe centre line of the tracks 30b to the main frame 30.

The main track frame 30 is similar to the track frame of existingcontinuous miners, but with an extension 37 on each side of the frontend to support the roof bolting machines 31. This is envisaged to be inthe form of a ledge 113 with a front plate 141 for additional rigidity.The front plate 114 is angled to allow the bolting machines 31 to beangled forward up to 10°, thereby keeping the unsupported roof to aminimum. The extensions 37 need to be sufficiently rigid, not only tocarry the weight of the bolters 31, but to provide the reaction to thethrust required for drilling.

The extensions 37, rigidly attached to the main frame 30, will provide astable bolting platform allowing roof support operations to be carriedout at the same time as coal cutting operations.

The tracks 30b are made as large as possible in order to obtain maximumstability and resistance to the thrust on the cutting head. The frame 30should resist all the reacting forces likely to be encountered withoutmovement.

The roof bolters 31 may be of a conventional type, and either hydraulicor pneumatic depending on the preference of the user. In practicehydraulic rigs require complex equipment on the machine because of thenecessity to provide adequate pump and oil reservoir capacity. Othertypes require only the mounting position to be provided. As shown inFIGS. 7 and 8 each roof bolter 31 comprises an upstanding frame 115incorporating hydraulic rams 101 and within which a drilling machine 116with drilling bit 118 is mounted for movement up and down the frame by achain drive 117 driven by a hydraulic motor 119. The upper end of theframe 115 has a pair of support members 120 adapted to engage beneaththe strap or bar which is to be bolted to the roof. If there is arequirement for angled bolts across the heading the bolters can bemounted on pivot joints 125 through yokes 124 on the bottoms of theframes 115 with the only drawback being that control of the bolterposition by hydraulic cylinders (not shown) would become more complex.

As shown the basic machine of this preferred embodiment carries fourroof bolters 31 for simultaneous operation. A further two bolters can bemounted (subject to the roadway width not being less than 5 m) althoughhydraulic capacity may be a drawback. In some situations, a shorter roofbolter or bolting rig could be mounted on a platform above the centreconveyor 28, to install short roof bolts.

When using hydraulic driven roof bolters 31, sufficient pump and oilreservoir capacity is necessary. Current hydraulic rigs require a supplyof approximately 2.25 liter/second. Added to the four roof bolters wouldbe the supply required to operate the various hydraulic motors andcylinders to give an overall total of the order of 20 liter/second. Thisorder of magnitude of supply requires the provision of large or numerouspumps, large oil reservoir capacity and attention to heat dissipation.Considerable weight will be required on the main frame 31 to providestability, in which case, all of this equipment would probably bemounted on or in the frame. If not, a power pack may be positioned nearthe face area with the hydraulic oil transmitted to the machine by atrailing hose system. The cutter head 21 may also be hydraulicallydriven and would have the additional advantage, that the only electricpower required at the face would be for lighting. The power pack wouldbe moved forward in a similar fashion to existing load centres and couldbe readily replaced in the event of breakdown.

Because the machine is designed for continuous operation, surge capacityshould be provided behind the machine so that delays waiting for shuttlecars are not encountered. A special surge car may be provided, which maybe track mounted, able to continually receive the output from the minerand transfer the load to a shuttle car in a very short time. This surgecar could be attached to the rear of the machine and be pulled along asit advances, although it would be preferable that it be self-propelledand independently operated.

For optimum operation, it is envisaged that directional control bemaintained by the use of a laser with a target mounted on the machine.

In order to improve stability of the machine it is probable that "stelljacks" 121 will be fitted on the outer ends of the face conveyor systemto bear against the ribs.

If it is found necessary, floor jacks 122 may be installed under therear of the main frame 30 as an aid to horizon control.

In order to deal with any dust problem in the area of the boltingmachines, where men will be working close to the cutting head, a dustextractor (not shown) is provided in the form of a vent duct withintakes along its length attached to a small auxiliary fan, and mountedalong the top of the face conveyor section 28a. This would exhaust intothe return air or through a scrubber into the air stream out by themachine.

In operation, the machine is positioned at the face with the sumpingrams 106 fully retracted, and both roof bolting and coal cuttingoperations commence simultaneously. The method of operation of thecutting head 21 will be the same as that for the Westfalia VMO8, with arelatively small sump followed by a combined trepanning and shearingoperation until the first increment of advance has been fully profiled.The cutting head 21 and conveyor 28, 28a would then be sumped forwardagain using the sumping rams 106, while the track frame 30 remainsstationary and roof bolting continues.

This cycle is repeated until the full one meter advance has been cut, bywhich time the roof bolting operations should be completed. The trackframe 30 would then be trammed forward, while the cutting head 21 andconveyor 28, 28a remain in position until the sumping rams 106 are againin the fully retracted position.

Cutting of a turn would be achieved by using the sideways cutting actionof the drum 24 on that side. By using a combination of advancing thecutting head with sumping rams 106, slewing the main frame on tracks30a, and with the ability to cut past the end of the face conveyor 28a,the full turn would be negotiated. However, at times, it may benecessary to stop cutting operations while bolting is carried out.

It has been calculated, that even without retractable sections on theface conveyor 28a, a turn could be negotiated with an inside radius ofabout 4.5 m.

If ventilation is a problem, an auxiliary blower system may be used withthe fan sited in the intake airway. The freshest air available wouldthen be delivered to the face without picking up any dust or methanemake from the roadside ribs.

However, the type of cutting action of the machine, being at acontinuous, relatively slow rate, is less onerous for ventilation thanthe present continuous miners which cut coal (and hence release gas) inshort bursts at a high rate.

Though the miner driver and roof bolter operators can be sitedrelatively remotely from the cutting head area, the bolting assistantswill be working close to the head at all times. The conveyor back plateheight should be sufficient to make it difficult to fall over into theconveyor. Guarding to increase this height can be provided, with areasonably open mesh, so that visibility for the miner drive is notobscured. A cowl behind the cutter drums to obstruct any material thrownback by the cutters 24 may also be provided.

With the machine of the present invention the time taken for roofsupport activity is significantly reduced, if not eliminated, Thus, fora 6 hour working shift with a cutting rate of 3.5 tonnes/min for 4hours, the total production would be 840 tonnes/shift (say 830 tonnes,allowing 10 tonnes left in the ribs). This represents a marked increaseover existing production rates which are typically of the order of 300to 350 tonnes/shift. Compared to a 350 tonnes/shift for, say, 150days/year represents an additional annual tonnage of 216,000 tonnes.

In addition, because the roadway mined would be narrower than is usuallypossible with existing continuous miners, and would be a fixed width, agreater proportion of the tonnage produced would represent distanceadvanced. (For example, for a 5 m wide roadway, each 17.5 tonnes in a2.5 m seam represents an advance of 1 m; for a 5.5 m roadway, 19.25tonnes are required for 1 m advance.) The main objective of developmentis usually to open up blocks for the economic process of pillarextraction, whether by longwall or some other method. A total of 840tonnes at 17.5 tonnes/m represents an advance/shift of 48 m; a total of350 tonnes at 19.25 tonnes/m represents an advance/shift of only 18.2 m.

Thus, the machine of the present invention provides a marked improvementin all aspects of the mining operation. The potential financial gainsfrom the increased productivity alone are great, apart from the increasein development rate which, at present, is a major factor in preventinglongwall systems from reaching their full potential.

Apart from the production benefits noted above there are a number ofother benefits inherent in the machine which are obtained:

(a) Because the machine cuts a narrow roadway with straight ribs, at arelatively slow and gentle rate, with supports set close to the face ina regular pattern, the roadway will be (and is likely to remain) farmore stable than roadways mined with existing equipment in the sameconditions. This will lead to a reduced likelihood of accidents fromfalls of material, reduced roadway maintenance costs and possiblyreduced initial support costs. In some cases it may be possible toeliminate timber supports altogether.

(b) The added roadway stability will enhance the performance of pillarextraction equipment, whichever method is used.

(c) In mines with weak floors the damage caused by continuous minersmoving from side to side in the face area will be eliminated.

We claim:
 1. A continuous mining machine, comprising a unitary mainframe mounted on tracks for mobility, said main frame having a forwardend and a rear end, a cutter head mounted on a sub-frame, meansconnecting said sub-frame to the forward end of said main frame, saidconnecting means including means for moving said sub-frame toward andaway from the front end of the said main frame, a trailing conveyorcarried by said main frame and extending rearwardly beyond the rear endof said main frame, leading conveyor means carried by said sub-frame tocollect mined material and convey it to said trailing conveyor, and aplurality of roof bolters each pivotally supported on said main frameadjacent the front thereof such as to be tiltable to allow each bolterto apply roof bolts at spaced apart positions transversely of thedirection of movement of the machine, wherein, as said sub-frame ismoved away from the front of said main frame and the cutter head mountedthereon operates to cut material to be mined, said roof bolters aresimultaneously operated to perform roof bolting operations close to theface of the mine.
 2. A continuous mining machine as claimed in claim 1,wherein said sub-frame is adapted to move toward and away from said mainframe by rams positioned between said sub-frame and said main frame. 3.A continuous mining machine is claimed in claim 2, wherein said rams arepivotably coupled to said sub-frame and said main frame.
 4. A continuousmining machine as claimed in claim 1, wherein said sub-frame is slidablymounted on said main frame via a pivotable joint and means are providedto tilt said sub-frame about said pivot to raise the cutter headsupported thereon above the ground when necessary.
 5. A continuousmining machine as claimed in claim 1, wherein said roof bolting meanscomprises a plurality of roof bolters pivotably supported on said mainframe so as to be tiltable toward the front of said machine.
 6. Acontinuous mining machine as claimed in claim 1, wherein said cutterhead is mounted on said sub-frame so as to be traversable laterally ofsaid machine and a first section of said conveyor means also extendslaterally of said machine whereby to collect mined material at thelaterally extreme positions of said cutter head.
 7. A continuous miningmachine as in claim 1 wherein said leading conveyor means includes azipper conveyor mounted on said sub-frame.
 8. A continuous miningmachine as in claim 1 wherein said trailing conveyor means is a slewconveyor.
 9. A continuous mining machine as claimed in claim 8, whereinsaid slew conveyor is pivotly supported on said main frame such as to betiltable upwardly or downwardly with respect thereto.